Polymer surfaces have been modified by exposure to ultraviolet and/or visible radiation while such surfaces are in contact with selected compounds (i.e., modifiers). In some cases, those compounds are organic, and are selected for their ability to participate in electron transfer reactions with a polymer film and/or sensitizer. The resultant modified polymer surface typically has organic residues corresponding to the selected organic compounds covalently bonded to the polymer film. Such residues, being organic, may be colored and/or may have a tendency to oxidize when exposed to atmospheric oxygen causing a change in one or more properties (e.g., surface energy) of the surface over time. This may be especially important for polymer films, such as fluorine-containing polymer (i.e., fluoropolymer) films, that may not otherwise oxidize under ambient conditions.
It would be desirable to have processes, capable of permanently modifying the surface of a polymeric substrate, such that the surface is not prone to discoloration and/or oxidation for long periods of time.
Fluoropolymers are a commercially useful class of materials. Fluoropolymers include, for example, crosslinked fluoroelastomers and semi-crystalline or glassy fluoropolymers. Fluoropolymers are generally of high thermal stability and are particularly useful at high temperatures. They may also exhibit extreme toughness and flexibility at very low temperatures. Many of these fluoropolymers are almost totally insoluble in a wide variety of solvents and are generally chemically resistant. Some have extremely low dielectric loss and high dielectric strength, and may have unique non-adhesive and low friction properties. Fluoroelastomers, particularly the copolymers of vinylidene fluoride with other ethylenically unsaturated halogenated monomers, such as hexafluoropropylene, have particular utility in high temperature applications, such as seals, gaskets, and linings.
Surface modification of fluoropolymers using inorganic compounds may be relatively slow and or difficult to carry out (e.g., involving many process steps). It would be desirable to have methods for enhancing the rate of such processes and the ease with which they may be carried out.
Multi-layer constructions containing a fluoropolymer enjoy wide industrial application. Such constructions find utility, for example, in fuel line hoses and related containers and hoses or gaskets in the chemical processing field. Adhesion between the layers of a multi-layered article may need to meet various performance standards depending on the use of the finished article. However, it is often difficult to establish high bond strengths when one of the layers is a fluoropolymer, in part, because of the non-adhesive qualities of fluoropolymers.
It would be desirable to have methods for improving the strength of adhesive bonds to polymeric substrates.